The present invention relates to a pressure resistant end shell for a container, as well as to a method and an apparatus for forming such an end shell. More particularly, this invention relates to an end shell for a container formed in such a method, and by an appropriate apparatus, that the end shell has a negative panel wall angle.
The prior art teaches various methods for increasing the pressure resistant capabilities of containers. Increasing the pressure resistance of containers is desirable for various reasons. First, containers having end shells of equivalent gauge can be made to withstand higher internal pressures. And, also, containers having end shells of thinner gauge can be made to withstand equivalent or higher pressures. Being able to reduce the gauge of the material used as end shells for containers, while maintaining adequate internal pressure resistance, has the significant advantage of material cost reduction.
One method of increasing the pressure resistant capabilities of a container is to increase the depth of the annular groove in an end shell, with respect to the central wall of the end shell. U.S. Pat. No. 4,031,837 teaches a method of reforming a conventional end shell by moving a drawing tool into a conventional annular groove while supporting the central wall of the end shell to draw the metal in the process of increasing the depth of the annular groove. U.S. Pat. No. 4,109,599 also teaches a method of forming a pressure resistant end shell for a container in which the thickness of the end shell is not reduced in a final forming operation.
Despite significant progress in the area of increasing the pressure resistant capabilities of end shells for containers, there is still a need and a demand for further improvement.
Accordingly, a new and improved pressure resistant end shell for a container, and a method and an apparatus for forming such an end shell are desired to further increase the pressure holding capabilities.